Brendan Smialowski/Getty Images(WASHINGTON) -- Sen. Bernie Sanders (I-Vt.) doesn't like what President Obama's budget could do to Social Security benefits. And he's not that happy that the White House is hosting a dozen Republican Senators for dinner Wednesday night, while progressives' invitations appear to have been lost in the mail.

Asked whether Obama ought to reach out more to liberals, including those like Sanders who are eager to chew up his budget, the senator joked: “Am I anxious to get a good free dinner? Absolutely, I am always open for a good free dinner.”

But "that invitation has not been offered," Sanders told ABC News in an interview on Pennsylvania Avenue just outside the White House gates. "He hasn't reached out to me, to the best of my knowledge, he hasn't reached out to progressives, and that is disappointing.”

Sanders is part of a group of progressive members of Congress, and interest groups, opposing the president’s budget. Following his interview with ABC News, he joined a rally in front of the White House to garner support for a petition calling on the president not to cut Social Security and Medicare benefits.

“People who have voted with the president, it's not just Bernie Sanders, are extremely disappointed with the president,” said Sanders, who points to unions, veterans’ organizations, and AARP as organizations that share his position. “They are saying, do not balance the budget on people who have lost their arms and legs defending this country.”

The senator went on to warn the president of the potential political backlash to his proposed budget cuts.

“I think we have the vast majority of the American people behind us, the president has got to know that, and the people that want to vote to cut Social Security or benefits for disabled vets are walking down a very perilous political path to my mind,” Sanders said.